U.S. patent number 6,432,259 [Application Number 09/461,682] was granted by the patent office on 2002-08-13 for plasma reactor cooled ceiling with an array of thermally isolated plasma heated mini-gas distribution plates.
This patent grant is currently assigned to Applied Materials, Inc.. Invention is credited to Jim Carducci, Evans Lee, Paul Luscher, Hamid Noorbakhsh, Siamak Salimian, Hongching Shan, Kaushik Vaidya, Michael Welch.
United States Patent |
6,432,259 |
Noorbakhsh , et al. |
August 13, 2002 |
Plasma reactor cooled ceiling with an array of thermally isolated
plasma heated mini-gas distribution plates
Abstract
A plasma reactor embodying the invention includes a wafer
support and a chamber enclosure member having an interior surface
generally facing the wafer support. At least one miniature gas
distribution plate for introducing a process gas into the reactor
is supported on the chamber enclosure member and has an outlet
surface which is a fraction of the area of the interior surface of
said wafer support. A coolant system maintains the chamber
enclosure member at a low temperature, and the miniature gas
distribution plate is at least partially thermally insulated from
the chamber enclosure member so that it is maintained at a higher
temperature by plasma heating.
Inventors: |
Noorbakhsh; Hamid (Fremont,
CA), Welch; Michael (Livermore, CA), Salimian; Siamak
(Sunnyvale, CA), Luscher; Paul (Sunnyvale, CA), Shan;
Hongching (San Jose, CA), Vaidya; Kaushik (Sunnyvale,
CA), Carducci; Jim (Sunnyvale, CA), Lee; Evans
(Milpitas, CA) |
Assignee: |
Applied Materials, Inc. (Santa
Clara, CA)
|
Family
ID: |
23833530 |
Appl.
No.: |
09/461,682 |
Filed: |
December 14, 1999 |
Current U.S.
Class: |
156/345.33;
118/723E; 118/724; 156/345.34; 156/345.44 |
Current CPC
Class: |
H01J
37/321 (20130101); H01J 37/3244 (20130101); H01J
37/32522 (20130101) |
Current International
Class: |
H01J
37/32 (20060101); H05H 001/00 (); C23C
016/00 () |
Field of
Search: |
;118/723I,723E,724,715
;156/345.33,345.34,345.44 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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838843 |
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Apr 1998 |
|
EP |
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877410 |
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Nov 1998 |
|
EP |
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838843 |
|
Jan 1999 |
|
EP |
|
WO 98/560027 |
|
Dec 1998 |
|
WO |
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WO 00/41212 |
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Jul 2000 |
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WO |
|
Primary Examiner: Mills; Gregory
Assistant Examiner: Hassanzadeh; P.
Attorney, Agent or Firm: Michaelson and Wallace Bach; Joseph
Allan; Ben
Claims
What is claimed is:
1. A plasma reactor for processing a semiconductor wafer,
comprising: a plasma source power applicator; a wafer support; a
chamber enclosure member having an interior surface generally
facing said wafer support; at least one miniature gas distribution
plate for introducing a process gas into said reactor and supported
on said chamber enclosure member and having an outlet surface which
is a fraction of the area of said wafer support; said chamber
enclosure member comprising coolant passages for maintaining said
chamber enclosure member at a low temperature; a thermally
resistant element between said miniature gas distribution plate and
said chamber enclosure member; and wherein said at least one
miniature gas distribution plate confronts said chamber enclosure
member along an interface, said thermally resistant element being
interposed substantially along said interface.
2. The reactor of claim 1 wherein said thermally resistant element
has a sufficiently low heat conductance so that plasma heating can
maintain said miniature gas distribution plate at a sufficiently
high temperature to prevent accumulation of polymer.
3. The reactor of claim 1 wherein said cooling passages are
sufficient to maintain said chamber enclosure at a temperature to
inhibit flaking of accumulated polymer therefrom.
4. The apparatus of claim 1 wherein said gas distribution plate is
of a sufficiently small size so that plasma heating thereof is
capable of maintaining said gas distribution plate at a
sufficiently high temperature to prevent accumulation of polymer
thereon.
5. The apparatus of claim 1 wherein said miniature gas distribution
plate comprises plural gas inlet holes having respective openings
at said outlet surface.
6. The apparatus of claim 5 wherein said plural gas inlet holes
extend through said miniature gas distribution plate, said chamber
enclosure member comprising a process gas supply manifold in
communication with said plural gas inlet holes.
7. The apparatus of claim 5 wherein said gas inlet holes are
elongate and extend angularly with respect to a perpendicular
direction to said outlet surface.
8. The apparatus of claim 7 wherein said inlet holes are angled
relative to said outlet surface so as to provide respective spray
patterns from said respective inlet holes which have a crossing
pattern.
9. The apparatus of claim 8 wherein said outlet surface has a
sufficiently small surface area so as to be contained within said
gas turbulent region.
10. The apparatus of claim 7 wherein said inlet holes are angled
relative to said outlet surface so as to provide respective spray
patterns from said respective inlet holes which have a vortex
pattern.
11. The apparatus of claim 7 wherein said inlet holes provide spray
patterns which enhance gas turbulence in a gas turbulent region
proximal said outlet surface.
12. The apparatus of claim 1 further a coolant source for
circulating coolant within said passages.
13. The apparatus of claim 1 further comprising an array of
miniature gas distribution plates on said chamber enclosure
member.
14. The apparatus of claim 13 wherein said chamber enclosure member
comprises a ceiling overlying said wafer support, said ceiling
having a surface area exceeding the surface area of said wafer
support, the outlet surface of each of said miniature gas
distribution plates being of an area at least about one order of
magnitude less than the surface area of said ceiling.
15. The apparatus of claim 14 further comprising plural holes in
the interior surface of said ceiling within which respective ones
of said miniature gas distribution plates are nested.
16. The apparatus of claim 15 wherein each of said miniature gas
distribution plates protrudes from the respective hole so that the
outlet surface of each of the gas distribution plates protrudes
below the interior surface of said ceiling by a distance d.
17. The apparatus of claim 16 wherein the interior surface of said
ceiling is waffled to provide better adhesion thereto of polymer
accumulated thereon.
18. The apparatus of claim 16 wherein said distance d is on the
order of a millimeter.
19. The apparatus of claim 18 wherein the diameter of each of said
miniature gas distribution plates is on the order of less than 1
cm, while the diameter of said ceiling is on the order of about 25
cm.
20. The apparatus of claim 1 wherein the thermal mass of said
miniature gas distribution plate is sufficiently small and the
thermal insulation thereof is sufficiently great so that the plasma
heating thereof maintains said miniature gas distribution plate
above a polymer condensation temperature, while said cooling system
is sufficient to maintain said ceiling below a polymer condensation
temperature.
21. The apparatus of claim 1 wherein said outlet surface is
generally facing a central processing region of said reactor.
22. The apparatus of claim 1 wherein said outlet surface comprises
one of: (1) a generally planar surface, or (2) a substantially
U-shaped surface exposed to a processing chamber.
23. A plasma reactor comprising: a chamber enclosure including a
ceiling, said enclosure defining a chamber interior; a wafer
support within said chamber interior and underlying said ceiling; a
plasma source power applicator; an array of plural miniature gas
distribution plates on the interior side of said ceiling, each of
said miniature gas distribution plates having an outlet surface
facing said chamber interior with plural gas inlet holes for
spraying respective streams of process gas into said chamber
interior, said outlet surface having an area less than a fraction
of the area of the interior of said ceiling; and wherein said
outlet surface is exposed to said chamber interior and generally
facing a central region of said chamber interior such that the
process gas is provided into the central region of the chamber
interior.
24. The reactor of claim 22 further comprising: a source of a
deposition precursor-containing process gas coupled to each of said
miniature gas distribution plates, said process gas being a
precursor of a deposition material having a condensation
temperature; wherein said miniature gas distribution plates are
susceptible of being heated to a temperature above said
condensation temperature by a plasma within chamber interior while
permitting said ceiling to remain at a temperature below said
condensation temperature.
25. The reactor of claim 24 further comprising waffling on the
interior surface of said ceiling, said waffling being sufficient to
promote adhesion of said deposition material on the ceiling
interior surface.
26. The reactor of claim 25 wherein said waffling comprises plural
bumps on said interior ceiling surface, said bumps having a typical
height on the order of about 1 mm at a bump-to-bump spacing on the
order of about 4 mm.
27. The reactor of claim 23 wherein said gas inlet holes are angled
relative to said outlet surface so as to enhance gas turbulence
produced by said respective streams of process gas in the vicinity
of said outlet surface.
28. The reactor of claim 27 wherein said gas inlet holes are angled
so as to provide a crossing pattern of said respective streams.
29. The reactor of claim 27 wherein said gas inlet holes are angled
so as to provide a vortex pattern of said respective streams.
30. The reactor of claim 23 further comprising a cooling system for
cooling said ceiling.
31. The reactor of claim 30 wherein said cooling system is
sufficient to maintain said ceiling below said condensation
temperature.
32. The reactor of claim 31 wherein cooling system comprising
coolant passages in said ceiling and a coolant source for
supporting coolant flow through said coolant passages.
33. The reactor of claim 23 further comprising thermal insulation
between each of said miniature gas distribution plates and said
ceiling.
34. The reactor of claim 33 wherein said thermal insulation is
sufficient to permit plasma heating of said miniature gas
distribution plates above said condensation temperature while said
ceiling is below said condensation temperature.
35. The reactor of claim 33 wherein said thermal insulation has a
thermal resistance on the order of that of aluminum nitride.
36. The reactor of claim 33 wherein said thermally resistant
element extends substantially along an interface between said
chamber enclosure and each of said miniature gas distribution
plates.
37. The reactor of claim 23 wherein said gas distribution plate is
of a sufficiently small size so that it is susceptible of being
heated above said condensation temperature by plasma heating.
38. The reactor of claim 23 wherein said gas distribution plate has
a diameter of about 0.25 inch.
39. The reactor of claim 23 wherein said gas distribution plate
protrudes beyond an interior surface of said chamber enclosure by a
fraction of the thickness of said gas distribution plate.
40. The reactor of claim 39 wherein said fraction is on the order
of about one-half.
41. The reactor of claim 23 wherein said outlet surface comprises
one of: (1) a generally planar surface, or (2) a substantially
U-shaped surface exposed to said chamber interior.
42. A showerhead plug for mounting on an interior side of a plasma
reactor chamber enclosure member, said plug comprising: plural gas
inlet holes for spraying a process gas into said reactor at an
outlet surface of said showerhead plug; said showerhead plug being
of a small fraction of the size of said chamber enclosure member;
and wherein said showerhead plug is adapted so that said outlet
surface is capable of being positioned exposed to and generally
facing a central region of said reactor chamber such that the
process gas is provided into the central region of the chamber
interior.
43. The plug of claim 42 further comprising: a thermally insulating
material for thermally insulating at least said outlet surface from
said chamber enclosure member.
44. The plug of claim 43 wherein said thermally resistant element
is capable of extending substantially along an interface between
said chamber enclosure member and said showerhead plug.
45. The plug of claim 42 wherein said chamber enclosure member
comprises a reactor chamber ceiling.
46. The plug of claim 42 wherein said plural gas inlet holes are
angled relative to said outlet surface to enhance gas turbulence in
the vicinity of said outlet surface.
47. The plug of claim 46 wherein said plural gas inlet holed
provide a vortex spray pattern.
48. The plug of claim 46 wherein said plural gas inlet holes
provide a crossing spray pattern.
49. The plug of claim 42 wherein said plug comprises a showerhead
body and thermal insulation between said body said ceiling.
50. The reactor of claim 49 wherein said thermal insulation is
sufficient to permit plasma heating of said showerhead plug above a
condensation temperature of a deposition precursor material
contained in a process gas while said ceiling is below said
condensation temperature.
51. The reactor of claim 50 wherein said showerhead plug is of a
sufficiently small size so that it is susceptible of being heated
above said condensation temperature by plasma heating.
52. The reactor of claim 49 wherein said thermal insulation has a
thermal resistance on the order of that of aluminum nitride.
53. The reactor of claim 42 herein said gas distribution plate has
a diameter of about 0.25 inch.
54. The reactor of claim 42 wherein said showerhead plug protrudes
beyond an interior surface of said chamber enclosure by a fraction
of the thickness of said showerhead plug.
55. The reactor of claim 54 wherein said showerhead plug protrudes
beyond an interior surface of said chamber by about 0.2 inches to
0.3 inches.
56. The plug of claim 42 wherein said outlet surface comprises one
of: (1) a generally planar surface, or (2) a substantially U-shaped
surface capable of being exposed to said plasma processing chamber
interior.
57. A plasma reactor comprising: a chamber enclosure including a
ceiling, said enclosure defining a chamber interior; a wafer
support within said chamber interior and underlying said ceiling; a
plasma source power applicator; an array of plural miniature gas
distribution plates on the interior side of said ceiling, each of
said miniature gas distribution plates having an outlet surface
facing said chamber interior with plural gas inlet holes for
spraying respective streams of process gas into said chamber
interior, said outlet surface having an area less than a fraction
of the area of the interior of said ceiling; wherein said gas inlet
holes are angled relative to said outlet surface so as to enhance
gas turbulence produced by said respective streams of process gas
in the vicinity of said outlet surface; and wherein said gas inlet
holes are angled so as to provide a crossing pattern of said
respective streams.
58. A plasma reactor comprising: a chamber enclosure including a
ceiling, said enclosure defining a chamber interior; a wafer
support within said chamber interior and underlying said ceiling; a
plasma source power applicator; an array of plural miniature gas
distribution plates on the interior side of said ceiling, each of
said miniature gas distribution plates having an outlet surface
facing said chamber interior with plural gas inlet holes for
spraying respective streams of process gas into said chamber
interior, said outlet surface having an area less than a fraction
of the area of the interior of said ceiling; wherein said gas inlet
holes are angled relative to said outlet surface so as to enhance
gas turbulence produced by said respective streams of process gas
in the vicinity of said outlet surface; and wherein said gas inlet
holes are angled so as to provide a vortex pattern of said
respective streams.
59. A showerhead plug for mounting on an interior side of a plasma
reactor chamber enclosure member, said plug comprising: plural gas
inlet holes for spraying a process gas into said reactor at an
outlet surface of said showerhead plug; said showerhead plug being
of a small fraction of the size of said chamber enclosure member;
wherein said plural gas inlet holes are angled relative to said
outlet surface to enhance gas turbulence in the vicinity of said
outlet surface; and wherein said plural gas inlet holes provide a
vortex spray pattern.
60. A showerhead plug for mounting on an interior side of a plasma
reactor chamber enclosure member, said plug comprising: plural gas
inlet holes for spraying a process gas into said reactor at an
outlet surface of said showerhead plug; said showerhead plug being
of a small fraction of the size of said chamber enclosure member;
wherein said plural gas inlet holes are angled relative to said
outlet surface to enhance gas turbulence in the vicinity of said
outlet surface; and wherein said plural gas inlet holes provide a
crossing spray pattern.
61. A plasma reactor for processing a semiconductor wafer, the
plasma reactor comprising: a) a chamber enclosure member defining a
processing chamber; b) a plasma source power applicator capable of
providing a plasma region within the processing chamber; c) a wafer
support within the processing chamber; d) the chamber enclosure
member being adapted to allow cooling of the enclosure member; e)
at least one showerhead plug embedded within the chamber enclosure
member, the at least one showerhead plug comprising: (1) an outlet
surface confronting the plasma region, the outlet surface having an
area less than a fraction of the area of the wafer support; and (2)
a plurality of gas distribution holes extending through the at
least one showerhead plug to the outlet surface; f) a thermally
resistant element located substantially along an interface between
the at least one showerhead plug and the chamber enclosure member;
and g) wherein the at least one showerhead plug and the thermally
resistant element are configured so as to allow plasma heating of
the showerhead plug to inhibit accumulation of deposits on the
outlet surface while the enclosure member is cooled to promote
accumulation of deposits on the enclosure member.
62. The plasma reactor of claim 61 wherein the plurality of gas
distribution holes extend angularly with respect to a perpendicular
direction to the outlet surface.
63. The plasma reactor of claim 62 wherein the plurality of gas
distribution holes are angle relative to the outlet surface such
that gas exiting from respective ones of the plurality of gas
distribution holes is directed at others of the plurality of gas
distribution holes.
64. The plasma reactor of claim 62 wherein the plurality of gas
holes are angled relative to the outlet surface such that gas
exiting from respective ones of the plurality of gas distribution
holes is directed so as to be capable of generating a vortex.
65. The plasma reactor of claim 62 wherein the plurality of gas
distribution holes are capable of providing spray patterns which
enhance gas turbulence in a gas turbulent region proximal the
outlet surface.
66. The plasma reactor of claim 65 wherein the outlet surface has a
sufficiently small surface area so as to be contained within the
gas turbulent region.
67. The plasma reactor of claim 61 wherein the chamber enclosure
member comprises a process gas supply manifold in communication
with the plurality of gas distribution holes.
68. The plasma reactor of claim 61 wherein the outlet surface is a
generally planar surface.
69. The plasma reactor of claim 61 wherein the outlet surface is a
substantially U-shaped surface.
70. The plasma reactor of claim 61 wherein the outlet surface is
flush with an interior surface of the enclosure member.
71. The plasma reactor of claim 61 wherein the outlet surface
protrudes below an interior surface of the enclosure member.
72. The plasma reactor of claim 71 wherein the outlet surface is
generally facing a central portion of the processing chamber.
73. The plasma reactor of claim 71 wherein the outlet surface is
generally facing a central portion of the processing chamber.
74. The plasma reactor of claim 61 wherein the thermally resistant
element extends substantially along an interface between opposing
surfaces of the chamber enclosure member and each of said miniature
gas distribution plates.
75. The plasma reactor of claim 61 wherein the outlet surface is
generally facing a central portion of the processing chamber.
76. A plasma reactor for processing a semiconductor wafer, the
plasma reactor comprising: a) a chamber enclosure member defining a
processing chamber; b) a plasma source power applicator capable of
providing a plasma region within the processing chamber; c) a wafer
support within the processing chamber; d) the chamber enclosure
member being adapted to allow cooling of the enclosure member; e)
at least one showerhead plug embedded within the chamber enclosure
member, the at least one showerhead plug comprising: (1) an outlet
surface confronting the plasma region; (2) a plurality of gas
distribution holes extending through the at least one showerhead
plug to the outlet surface; (3) wherein the outlet surface is
limited in area so that the area is contained within a region in
which turbulence from injected gas from the plurality of gas
distribution holes inhibits accumulation of deposits thereon; and
(4) wherein the area of outlet surface is a fraction of the area of
the wafer support; f) a thermally resistant element located
substantially along an interface between the at least one
showerhead plug and the chamber enclosure member; and g) wherein
the at least one showerhead plug and the thermally resistant
element are configured so as to allow plasma heating of the
showerhead plug to inhibit accumulation of deposits on the outlet
surface while the enclosure member is cooled to promote
accumulation of deposits on the enclosure member.
77. The plasma reactor of claim 76 wherein the plurality of gas
distribution holes extend angularly with respect to a perpendicular
direction to the outlet surface.
78. The plasma reactor of claim 77 wherein the plurality of gas
distribution holes are angled relative to the outlet surface such
that gas exiting from respective ones of the plurality of gas
distribution holes is directed at others of the plurality of gas
distribution holes.
79. The plasma reactor of claim 76 wherein the plurality of gas
distribution holes are angled relative to the outlet surface such
that gas exiting from respective ones of the plurality of gas
distribution holes is directed so as to be capable of generating a
vortex.
80. The plasma reactor of claim 76 wherein the chamber enclosure
member comprises a process gas supply manifold in communication
with the plurality of gas distribution holes.
81. The plasma reactor of claim 76 wherein the outlet surface is a
generally planar surface.
82. The plasma reactor of claim 76 wherein the outlet surface is a
substantially U-shaped surface.
83. The plasma reactor of claim 76 wherein the outlet surface is
flush with an interior surface of the enclosure member.
84. The plasma reactor of claim 76 wherein the outlet surface
protrudes below an interior surface of the enclosure member.
85. The plasma reactor of claim 84 wherein the outlet surface is
positioned generally facing a central region of the processing
chamber.
86. The plasma reactor of claim 85 wherein each of the plurality of
miniature gas distribution plugs confronts the chamber enclosure
member along an interface, said thermally resistant element being
interposed substantially along said interface.
87. The plasma reactor of claim 76 wherein each of the plurality of
miniature gas distribution plugs confronts the chamber enclosure
member along an interface, said thermally resistant element being
interposed substantially along said interface.
88. The plasma reactor of claim 76 wherein the outlet surface is
generally facing a central region of the processing chamber.
89. A plasma reactor comprising: a) a chamber enclosure member
defining a processing chamber; b) a plasma source power applicator
capable of providing a plasma region within the processing chamber;
c) a wafer support within the processing chamber; d) the chamber
enclosure member being adapted to allow cooling of the enclosure
member; e) an array of plural miniature gas distribution plates
embedded within the chamber enclosure member, each of the miniature
gas distribution plates comprising: (1) an outlet surface
confronting the chamber interior, the outlet surface having an area
less than a fraction of the area of the chamber enclosure member;
and (2) a plurality of holes extending through each of the
miniature gas distribution plugs to the outlet surface; f) a
thermally resistant element between each of the miniature gas
distribution plugs and the chamber enclosure member; and g) wherein
the miniature gas distribution plugs and the thermally resistant
elements are configured such that the thermally resistant element
is located substantially along an interface between the chamber
enclosure and the miniature gas distribution plugs so as to allow
plasma heating of the miniature gas distribution plugs to inhibit
accumulation of deposits on the outlet surface while the enclosure
member is cooled to promote accumulation of deposits on the
enclosure member.
90. The plasma reactor of claim 89 wherein the plurality of holes
extend angularly with respect to a perpendicular direction to the
outlet surface.
91. The plasma reactor of claim 90 wherein the plurality of holes
are at least one of: (a) angled relative to the outlet surface such
that gas exiting from respective ones of the plurality of holes is
directed at others of the plurality of holes, or (b) angled
relative to the outlet surface such that gas exiting from
respective ones of the plurality of holes is directed so as to be
capable of generating a vortex.
92. The plasma reactor of claim 90 wherein the plurality of holes
are capable of providing spray patterns which enhance gas
turbulence in a gas turbulent region proximal the outlet surface,
and wherein the outlet surface has a sufficiently small surface
area so as to be contained within the gas turbulent region.
93. The plasma reactor of claim 89 wherein the chamber enclosure
member comprises a process gas supply manifold in communication
with the plurality of holes.
94. The plasma reactor of claim 89 wherein the outlet surface is a
generally planar surface.
95. The plasma reactor of claim 89 herein the outlet surface is a
substantially U-shaped surface.
96. The plasma reactor of claim 89 wherein the outlet surface is
flush with an interior surface of the enclosure member.
97. The plasma reactor of claim 89 wherein the outlet surface
protrudes below an interior surface of the enclosure member.
98. The plasma reactor of claim 97 wherein the outlet surface is
generally facing a central region of the processing chamber.
99. The plasma reactor of claim 98 wherein each of the miniature
gas distribution plugs confronts the chamber enclosure member along
an interface, said thermally resistant element being interposed
substantially along said interface.
100. The plasma reactor of claim 89 wherein each of the plurality
of miniature gas distribution plugs confronts the chamber enclosure
member along an interface, said thermally resistant element being
interposed substantially along said interface.
101. The plasma reactor of claim 89 wherein the outlet surface is
generally facing a central region of the processing chamber.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The invention is related to a plasma reactor for processing a
semiconductor wafer using polymer precursor gases such as
fluorocarbon gases, and in particular to a gas distribution plate
and ceiling thereof.
2. Background Art
In plasma processing employed in the fabrication of semiconductor
microelectronic integrated circuits, a semiconductor wafer is
immersed in a plasma inside the chamber of a plasma reactor. The
reactor may be thus employed to carry out any one of various
processes on the wafer, such as chemical vapor deposition or
reactive ion etching. In certain plasma etch processes carried out
in such reactors, the upper most layer (the layer to be etched) may
have a lower etch rate than the underlying layer (which must not be
etched in most cases). This presents an especially challenging
problem because there would be no etch selectivity (or an inverse
selectivity) of the upper layer to the lower layer. This situation
is characteristic of a plasma process for etching a dielectric
layer overlying another layer such as a semiconductor layer (e.g.,
a silicon dioxide layer overlying a polysilicon layer) using a
process gas containing an etchant such as fluorine or fluoride
compounds. The problem has been solved by using a fluoride compound
such as a fluorocarbon gas or a fluoro-hydrocarbon gas which, upon
ionization, tends to break up into fluorine-containing etchant
species and polymer precursor species. The polymer precursor
species provide the requisite etch selectivity because it tends to
accumulate as a hard polymer film on non-oxygen containing
materials (such as the underlying polysilicon layer) but does not
accumulate on oxygen-containing materials (such as the overlying
silicon dioxide layer). Thus, the underlying layer is protected
from the etchant by the polymer layer while the overlying layer is
left exposed to the etchant, so that the process has a net etch
selectivity of the overlying layer.
The problem is that the polymer accumulates on the interior reactor
surfaces, including the ceiling of the chamber. Typically, the
ceiling consists of a gas distribution plate with gas distribution
inlets or orifices through which the process gas must be sprayed
into the reactor chamber for uniform distribution. The plate must
be formed of materials such as quartz which are suitable for
carrying the etchant-containing process gases. Such materials do
not readily lend themselves to temperature control, and therefore
the center of the gas distribution plate tends to be very hot due
to plasma heating while the perimeter tends to be colder. The
polymer accumulates as a solid film in the colder perimeter region
and cannot accumulate in the hot center region. Between these two
regions is a transition region where the polymer tends to
accumulate as a fine powder, which tends to flake onto the wafer
and create contamination. This requires that the gas distribution
plate be replaced periodically. The gas distribution plate is on
the order of the diameter of the wafer (e.g., 9 inches or 14
inches) and its replacement is expensive due to the cost of the
item as well as the non-productive time during which the reactor is
disassembled for removal and replacement of the gas distribution
plate. However, periodic removal and replacement of the gas
distribution plate is not a solution to the problem, as flaking of
any accumulated polymer from the gas distribution plate can occur
any time up to the replacement of the plate.
One solution to this problem might be to cool the entire gas
distribution plate so that the polymer deposited thereon is
entirely of a hard consistency and will not flake. However, this
would eventually block the gas inlets, stopping the inflow of the
process gas. Another solution might be to heat the entire gas
distribution plate sufficiently to prevent any polymer from
accumulating thereon. However, this would expose the entire gas
distribution plate to bombardment from the plasma and much faster
wear.
Therefore, there is a need for a gas distribution plate which is
not susceptible to accumulation of polymer or the flaking of
accumulated polymer onto the wafer.
SUMMARY OF THE INVENTION
A plasma reactor embodying the invention includes a wafer support
and a chamber enclosure member having an interior surface generally
facing the wafer support. At least one miniature gas distribution
plate for introducing a process gas into the reactor is supported
on the chamber enclosure member and has an outlet surface which is
a fraction of the area of the interior surface of said wafer
support. A coolant system maintains the chamber enclosure member at
a low temperature, and the miniature gas distribution plate is at
least partially thermally insulated from the chamber enclosure
member so that it is maintained at a higher temperature by plasma
heating.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a conventional plasma reactor including a gas
distribution plate of the prior art.
FIG. 2 is a cross-sectional cut-away view of a plasma reactor
including a water-cooled ceiling and an array of thermally isolated
mini-gas distribution plates embodying the invention.
FIG. 3 is a plan view of the ceiling interior surface corresponding
to FIG. 2.
FIG. 4 is a plan view of an individual mini-gas distribution plate
of the invention having angled gas inlets providing a preferred
vortex pattern of gas spray.
FIG. 5 is a cross-sectional cut-away view corresponding to FIG.
4.
FIG. 6 illustrates an alternative spray pattern corresponding to
FIG. 4.
FIG. 7 is an enlarged cut-away cross-sectional view corresponding
to FIG. 2.
FIG. 8 is an view corresponding to FIG. 7 illustrating a method of
fastening the mini-gas distribution plate on the ceiling.
FIG. 9 illustrates an alternative embodiment of the invention
having a mini-gas distribution plate mounted on the side wall of
the reactor chamber.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A reactor embodying the present invention has a cooled ceiling
formed preferably of a good thermal conductor such as metal and an
array of mini-gas distribution plates embedded therein, the gas
distribution plates being thermally isolated from the cooled
ceiling. The ceiling is sufficiently cooled so that polymer
accumulates thereon as a solid film with little or no tendency to
flake off, while the mini-gas distribution plates reach a
sufficiently high temperature from plasma-heating so that no
polymer accumulates thereon. Thus, neither the ceiling nor the
array of mini-gas distribution plates harbors polymer having a
tendency to flake. As a result, the necessity for replacement of
internal chamber parts (such as the ceiling or the mini-gas
distribution plates) is greatly reduced if not eliminated.
Each mini-gas distribution plate has plural gas injection holes
connected to a common manifold within the plate. The area of each
of the mini-gas distribution plates facing the plasma is limited so
that: (1) the area is contained within a region in which the
turbulence from the injected gas in the vicinity of the inlets
prevents or impedes polymer accumulation, and (2) the size or
thermal mass of the mini-gas distribution plate is sufficiently low
to allow rapid plasma-heating of the plate. In order to enhance the
gas turbulence across the area of the plate, the gas injection
holes in each mini-gas distribution plate are angled relative to
the surface of the plate facing the chamber interior. Preferably,
the gas injection holes are angled so that the gas injection
streams from adjacent holes cross one another or together form a
vortex pattern. In a preferred embodiment, the mini-gas
distribution plates extend slightly out from the surface of the
ceiling, to enhance plasma-heating thereof and to enhance gas
injection turbulence. Preferably, the mini-gas distribution plates
are each a relatively small fraction of the area of the entire
ceiling.
FIG. 1 illustrates a conventional plasma reactor chamber 100 having
a cylindrical side wall 105 supporting a ceiling 110 consisting of
a large gas distribution plate 115. The gas distribution plate 115
covers a major portion of the ceiling 110. The gas distribution
plate has a gas manifold 120 from which plural gas inlets 125
extend downwardly to the reactor chamber interior. The gas
distribution plate 115 overlies a wafer support 130 on which a
semiconductor wafer 135 is mounted. The gas distribution plate 115
has a diameter generally corresponding to that of the wafer 135,
and may be on the order of 9 inches or 14 inches in diameter.
Process gas is supplied to the gas distribution plate manifold by a
process gas source 140 through a pump 145. The pressure within the
chamber is maintained at a desired vacuum level by a vacuum pump
150. For capacitive coupling of RF power to the plasma within the
chamber 100, RF power is applied to the wafer support 130 by an RF
generator 160 through an impedance match circuit 165. The ceiling
110 or the gas distribution plate 115 may include a conductive
material which is grounded to provide a an RF return.
For a reactive ion etch process to be carried out on a dielectric
layer, the gas source can provide a fluoro-hydrocarbon gas, in
which case a polymer layer forms on a major portion of the gas
distribution plate 115. Heating from the plasma generally keeps the
center portion of the gas distribution plate too hot to accumulate
any polymer, while the peripheral edge portion of the gas
distribution plate is sufficiently cool to permit a hard film of
polymer to accumulate thereon. An intermediate annular portion 170
of the gas distribution plate 115 is typically at an intermediate
temperature at which the polymer can accumulate on the surface but
cannot form a hard film. Instead, in the intermediate region 170
the polymer tends to be powdery and flakes easily, leading to
contamination of the wafer 135. Therefore, the gas distribution
plate 115 must be replaced frequently.
The foregoing problems are overcome in the present invention.
Referring to FIGS. 2 and 3, a plasma reactor embodying the present
invention has a water-cooled ceiling 210 in which there are
embedded an array of showerhead plugs or mini-gas distribution
plates 220. Each mini-gas distribution plate 220 is formed of a
semi-metal such as silicon or a dielectric such as silicon dioxide
(quartz) or sapphire, and has plural gas inlets 225 through which
process gas is sprayed into the reactor chamber interior.
Preferably, the mini-gas distribution plates 220 are thermally
insulated from the water-cooled ceiling 210, so that they are
readily heated by the plasma within the chamber. Each gas
distribution plate 220 is sufficiently small relative to the
ceiling--has a sufficiently small thermal mass--so as to be rapidly
heated by the plasma upon plasma ignition. (For example, the
ceiling 210 may have a diameter in a range of 9 inches to 14
inches, while the gas distribution plate has an exposed diameter on
the order of about 0.25-0.5 inch. As a result, the plasma heats
each mini-gas distribution plate 220 to a sufficiently high
temperature to prevent any accumulation of polymer thereon. The
advantage is that the gas inlets 225 of each mini-gas distribution
plate 220 can be kept clear of polymer.
Preferably, the diameter of each mini-gas distribution plate 220 is
sufficiently small so that the entire bottom surface 220a of the
gas distribution plate 220 is enveloped within a region of gas flow
turbulence of the process gas spray from the inlets 225. Thus, for
example, each mini-gas distribution plate 220 has an exposed
diameter on the order of about 0.25-0.5 inch. This region has
sufficient gas turbulence to retard or prevent the accumulation of
polymer on the surface 220a.
Referring to FIGS. 4 and 5, the gas turbulence around the bottom
surface 220a is enhanced by introducing a crossing pattern of gas
spray paths from the plural gas inlets 225 of the mini-gas
distribution plate 220. The embodiment of FIGS. 4 and 5 provides a
vortex pattern (indicated by the arrows of FIG. 4). This is
accomplished by drilling each of the gas inlets 225 at an angle A
relative to the outlet surface 220a of the mini-gas distribution
plate 220. Preferably, the angle A is in the range of about 20
degrees to 30 degrees. In an alternative embodiment illustrated in
FIG. 6, the gas spray paths of the plural gas inlets 225 are
directed at other inlets in order to enhance the gas
turbulence.
As a further aid in inhibiting the accumulation of polymer on the
mini-gas distribution plates 220, the outlet surface 220a of the
plate 220 extends slightly below the surface of the ceiling 210 by
a distance d, as shown in FIG. 7. The distance d is preferably
about 0.02 inch to 0.03 inch or a fraction of the thickness of the
gas distribution plate 220. The enlarged cross-sectional view of
FIG. 7 illustrates one preferred implementation in which the gas
inlets 225 are angled holes passing entirely through the mini-gas
distribution plate 220. Process gas is supplied to the gas inlets
225 by a common manifold 230 formed in the ceiling 210. A water
jacket 240 of the water-cooled ceiling 210 is also shown in the
drawing of FIG. 7. Preferably, a thermal insulation layer 250,
which may be aluminum nitride for example, is trapped between the
mini-gas distribution plate 220 and the ceiling 210.
The water-cooled ceiling 210 is maintained at a sufficiently low
temperature so that polymer accumulates on the entire ceiling as a
very hard film which is virtually immune from flaking or
contributing contamination to the chamber interior. The thermally
isolated mini-gas distribution plates 220 are heated by the plasma
to a sufficiently high temperature to inhibit accumulation of
polymer thereon. Thus, the gas inlets 225 are kept clear of any
polymer. The small size of the mini-gas distribution plates 220 not
only enables the plasma to heat them to the requisite temperature.
It also permits the concentration of gas inlets 225 over the small
surface 220a to provide sufficient gas turbulence to further
inhibit the accumulation of polymer on the surface 220a or inlets
225. The gas turbulence is enhanced by providing a crossed or
vortex pattern of gas spray paths from each of the gas inlets 225
of the mini-gas distribution plate 220, and having the outlet
surface 220a below the ceiling 210. The combination of all of the
foregoing features prevents any observable accumulation of polymer
on any portion the mini-gas distribution plate 220.
In a preferred embodiment, there are four mini-gas distribution
plates 220 mounted on the ceiling 210 at four symmetrically spaced
locations overlying the periphery of the wafer 135. of course,
additional mini-gas distribution plates may be provided in other
embodiments, or their placement modified from the arrangement
illustrated in FIG. 5.
The advantage is that the ceiling and the gas distribution plate
need not be periodically replaced, at least not as frequently as in
the prior art, a significant advantage. Moreover, the system is
more immune from contamination from polymer flaking regardless of
the frequency with which the ceiling and gas distribution plates
are replaced.
FIG. 8 illustrates one mode for mechanically holding the mini-gas
distribution plate 220 in place on the ceiling 210. The mini-plate
220 has an annular ear 280 extending radially from its periphery.
The ceiling 210 has a hole 290 in which the mini-plate 220 is
nested, the ceiling 210 having upper and lower sections 210-1,
210-2 joined together by a threaded fastener 295. Each section
210-1, 210-2 has an annular shelf 210-1a, 210-2a which together
form an annular pocket 297 for receiving and holding the annular
ear 280.
In a preferred embodiment, polymer flaking from the ceiling 210 is
inhibited not only by cooling the ceiling but, in addition, by
providing a "waffled" surface on the ceiling. The waffled surface,
partially illustrated in FIG. 3, consists of an array of 1 mm
half-spherical "bumps" 300 spaced apart by about 4 mm. The bumps
300 are arrayed in this manner across the entire interior surface
of the ceiling 210. They tend to force the solid polymer film
accumulated thereon to form local crystalline regions which are
less susceptible to cracking than a large crystalline region.
While the invention has been described with reference to a
preferred embodiment in which the mini-gas distribution plates are
mounted in the reactor chamber ceiling, in an alternative
embodiment mini-gas distribution plates may be mounted at other
locations within the chamber, such as the chamber side wall, as
illustrated in FIG. 9. In this alternative embodiment, the side
wall 105 preferably is water-cooled for the same reasons that the
ceiling 210 is water cooled as explained above. The mini-gas
distribution plates 220 on the side wall 105 may be provided in
addition to or in lieu of the gas distribution plates 220 on the
ceiling 210.
While the invention has been described in detail by specific
reference to preferred embodiments, it is understood that
variations and modifications may be made without departing from the
true spirit and scope of the invention.
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